Zirconium under pressure: phase transitions and thermodynamics
Abstract
In this paper, the fullpotential linearized augmented planewave (LAPW) method within the generalized gradient approximation (GGA) was used to calculate the effect of hydrostatic pressure at zero temperature on the 4d transition metal zirconium. For the hexagonal closepacked (hcp), omega (ω), and bodycentred cubic (bcc) structures the enthalpy, H = E+pV, was calculated as a function of pressure p. We obtained an ω to bcc transition pressure of 28.2 GPa. Temperaturedependent contributions were obtained from tightbinding calculations of the phonons in the quasiharmonic approximation and were used to calculate the Gibbs free energy as a function of both temperature T and pressure for these three structures. From the comparison of these free energies the phase boundaries were calculated in the Tp phase diagram, and compared to the experimentally determined boundaries. We discuss the importance of anharmonicity for understanding the material properties of zirconium, and limitations of quasiharmonic phonon theories for predicting phase transformations.
 Publication:

Journal of Physics Condensed Matter
 Pub Date:
 February 2006
 DOI:
 10.1088/09538984/18/5/001
 Bibcode:
 2006JPCM...18.1483S